In western Illinois, ComEd is tapping a rarely used technique to fast-track community solar installations — working with, not against, environmental groups and solar project developers.

For years, utilities have explored the concept of flexible interconnection, in which solar projects are allowed to come online even when, by the books, there’s not enough space on the grid for these arrays. In return, these solar farms must promise to curtail output during the handful of hours each year when their production would overwhelm power lines and substations.

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Historically, utilities and solar developers have struggled to establish the basic mutual trust required to move a flexible interconnection program forward, Weaver said. Utilities are often skeptical that solar farms will reliably cut back as promised during those key hours of potential grid overload. Meanwhile, solar developers suspect utilities will force them offline more than is absolutely necessary.

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Both the utility and solar developers had to make some compromises, Weaver said. But that effort bore its first fruit last November, when 27 megawatts of community solar was green-lit in a region where it would have been excluded by traditional processes. Another 25 megawatts of projects were approved in February.

This coordinated approach is now gaining some momentum in Maryland, Massachusetts, New York, and other states where community solar is struggling, said Nikhil Balakumar, Eclipse’s CEO and founder.

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But this is easier said than done. Utilities can’t perfectly predict how often demand will peak. They need flexibility to handle unexpected changes and respond to emergencies. A major storm or flood could knock out an entire substation for months, leaving other parts of the grid straining to supply power until it’s repaired.

That uncertainty constrains utilities from setting guaranteed limits on how often they’ll ask solar projects to curtail their generation. But for solar developers, ​“projects aren’t financeable if curtailment is unpredictable,” Weaver said. ​“We need certain details to be able to literally take to the bank.”

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Solar developers calculated that they — and their investors — could bear having about 5% of their annual solar production curtailed. They conceded that ComEd couldn’t guarantee it would stick to that curtailment limit. But if the utility was willing to share historical data on how often its grid was likely to face overloads, developers could use that to convince those investors that the risk was worth taking.

That wasn’t the solar industry’s initial ask, Balakumar noted. Solar developers started out asking for ​“some sort of fund that compensates us if you do go over 5%,’” he said. But ComEd pays for the power it purchases by passing those costs on to its customers — and the prospect of charging customers for power that didn’t actually get onto the grid was a nonstarter for consumer advocates and regulators.

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The flexible and collaborative approach that ComEd and solar developers have undertaken stands in contrast to some much slower processes in other states. In California, for example, it took nearly four years between regulators ordering utilities to make flexible interconnection possible and finalizing the rules that allow it to happen — and California still hasn’t created a workable community solar program to make use of those rules.